U.S. patent number 11,105,963 [Application Number 15/454,195] was granted by the patent office on 2021-08-31 for optical systems with adjustable lenses.
This patent grant is currently assigned to Apple Inc.. The grantee listed for this patent is Apple Inc.. Invention is credited to Cheng Chen, Yuan Chen, Zhibing Ge, Michael Slootsky, Shuang Wang, Bennett S. Wilburn.
United States Patent |
11,105,963 |
Chen , et al. |
August 31, 2021 |
Optical systems with adjustable lenses
Abstract
Optical systems may have tunable lenses with focal lengths that
are adjusted by control circuitry. A display may produce image
light that is received by a tunable lens. The display may be
transparent so that light from objects can pass through the display
and be received by the tunable lens. The tunable lens may include a
birefringent lens element and a polarization rotator and may
receive light that has been linearly polarized by passing through a
linear polarizer. The polarization rotator may be operable in a
first state in which the polarization of light passing through the
polarization rotator is not rotated and a second state in which the
polarization of light passing through the polarization rotator is
rotated by 90.degree.. The birefringent lens element may be formed
from a cured liquid crystal polymer or other polymer and may have a
liquid crystal additive to enhance birefringence.
Inventors: |
Chen; Yuan (Santa Clara,
CA), Wilburn; Bennett S. (San Jose, CA), Chen; Cheng
(San Jose, CA), Slootsky; Michael (Santa Clara, CA),
Wang; Shuang (Sunnyvale, CA), Ge; Zhibing (Sunnyvale,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Assignee: |
Apple Inc. (Cupertino,
CA)
|
Family
ID: |
77465185 |
Appl.
No.: |
15/454,195 |
Filed: |
March 9, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15381882 |
Dec 16, 2016 |
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62305811 |
Mar 9, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
15/14 (20130101); G02B 3/14 (20130101); G02B
5/20 (20130101); G02F 1/294 (20210101); G02B
30/25 (20200101); G02B 27/288 (20130101); G02B
7/08 (20130101); G02B 27/286 (20130101) |
Current International
Class: |
G02F
1/29 (20060101); G02B 15/14 (20060101); G02B
30/25 (20200101); G02B 5/20 (20060101); G02B
3/14 (20060101); G02B 27/28 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2003032066 |
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Apr 2003 |
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WO |
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2014176695 |
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Nov 2014 |
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WO |
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Other References
Kirby et al., "Adaptive lenses based on polarization modulation",
Proc. SPIE 6018, 5th International Workshop on Adaptive Optics for
Industry and Medicine, 601814 (Jun. 8, 2006);
doi:10.1117/12.669373; http://dx.doi.org/10.1117/12.669373. cited
by applicant.
|
Primary Examiner: Nguyen; Thanh Nhan P
Attorney, Agent or Firm: Treyz Law Group, P.C. Treyz; G.
Victor Guihan; Joseph F.
Parent Case Text
This application is a continuation of U.S. patent application Ser.
No. 15/381,882, filed Dec. 16, 2016, and U.S. provisional patent
application No. 62/305,811, filed Mar. 9, 2016, which are hereby
incorporated by reference herein in their entireties.
Claims
What is claimed is:
1. A system, comprising: a display having an array of pixels that
creates images; a birefringent polymer lens; a polarization
rotator, wherein light from the images passes through the
polarization rotator and the birefringent polymer lens in that
order; and control circuitry that places the polarization rotator
alternately in first and second states, wherein the light passes
through the polarization rotator without rotation when the
polarization rotator is in the first state and wherein the light
passes through the polarization rotator with a 90.degree.
polarization rotation when the polarization rotator is in the
second state, wherein the polarization rotator comprises a liquid
crystal polarization rotator, wherein the birefringent polymer lens
comprises liquid crystal material in a cured polymer, wherein the
birefringent polymer lens comprises one of a plurality of
birefringent polymer lenses, wherein the polarization rotator
comprises one of a plurality of polarization rotators, and wherein
the system includes a plurality of stacked tunable lenses each of
which includes a respective one of the plurality of birefringent
polymer lenses and each of which includes a respective one of the
plurality of polarization rotators.
2. The system defined in claim 1 wherein the polarization rotator
comprises a twisted nematic liquid crystal polarization
rotator.
3. The system defined in claim 1 wherein the display comprises a
transparent display and wherein light from an external object
passes through the display and through the polarization
rotator.
4. The system defined in claim 1 further comprising a linear
polarizer that linearly polarizes light entering the polarization
rotator.
5. The system defined in claim 1 wherein the birefringent polymer
lens comprises first and second liquid crystal alignment
layers.
6. The system defined in claim 5 wherein the liquid crystal
material in the cured polymer is interposed between the first and
second liquid crystal alignment layers.
7. The system defined in claim 1, wherein the polarization rotator
is interposed between the display and the birefringent polymer
lens.
8. A tunable lens, comprising: a birefringent lens element; a
liquid crystal polarization rotator; a linear polarizer that
polarizes light entering the liquid crystal polarization rotator to
produce light with a linear polarization, wherein the liquid
crystal polarization rotator is operable in a first state in which
the linear polarization of the light is not rotated by the liquid
crystal polarization rotator and the birefringent lens element has
a first focal length and a second state in which the linear
polarization of the light is rotated by the liquid crystal
polarization rotator and the birefringent lens element has a second
focal length that is different than the first focal length; and a
polymer layer on the birefringent lens element, wherein the
birefringent lens element is characterized by an ordinary index of
refraction and an extraordinary index of refraction, and wherein
the polymer layer has an index of refraction equal to the ordinary
index of refraction.
9. The tunable lens defined in claim 8 wherein the liquid crystal
polarization rotator comprises a twisted nematic polarization
rotator.
10. The tunable lens defined in claim 8 wherein the birefringent
lens element comprises a polished birefringent crystal.
11. A system, comprising: control circuitry; a display coupled to
the control circuitry that produces image light; and a plurality of
stacked tunable lenses that receive the image light, wherein each
of the tunable lenses has a respective tunable focal length,
wherein each of the stacked tunable lenses comprises a birefringent
polymer lens element and a polarization rotator, wherein the
control circuitry is configured to control the polarization rotator
of each tunable lens to select an overall focal length for the
plurality of stacked tunable lenses, and wherein the control
circuitry is configured to repeatedly switch the overall focal
length in synchronization with images being displayed on the
display.
12. The system defined in claim 11 wherein the polarization rotator
comprises first and second transparent electrodes and a layer of
liquid crystal material interposed between the first and second
transparent electrodes and wherein the birefringent polymer lens
elements each include a pair of liquid crystal alignment
layers.
13. The system defined in claim 11 wherein the birefringent polymer
lens elements each include a plurality of ring-shaped electrodes.
Description
BACKGROUND
This relates generally to optical systems and, more particularly,
to optical systems with adjustable lenses.
Cameras, display projectors, and other optical systems have lenses.
It may sometimes be desirable to adjust a lens. For example, it may
be desirable to adjust the focal length of a zoom lens or it may be
desirable to focus a lens. Many optical systems are provided with
manually adjustable lens mounts that allow lens adjustments such as
focal length adjustments to be made. Motors and other electrically
controllable elements may also be used in making lens
adjustments.
Optical systems with adjustable lenses such as these may be bulky
and may respond more slowly than desired to control commands. It
would therefore be desirable to be able to provide improved optical
systems with adjustable lenses such as compact electrically
adjustable lenses.
SUMMARY
Optical systems may have adjustable lenses. The adjustable lenses
may have focal lengths that are adjusted by control circuitry.
Adjustable lenses may be used in adjusting magnification and focus
in optical systems, may be used in optical systems with displays,
and may be used in other optical systems.
A display in an optical system may produce images. The display may
be transparent so that light from external objects can pass through
the display. Light from images on the display and external objects
can pass through an adjustable lens before reaching a viewer. The
adjustable lens may be configured to exhibit different focal
lengths.
The adjustable lens may include a birefringent lens element and a
polarization rotator. Light received by the polarization rotator
may be passed through a linear polarizer before being received by
the polarization rotator. The polarization rotator may be operable
in a first state in which the polarization of light passing through
the polarization rotator is not rotated by the polarization rotator
and a second state in which the polarization of light passing
through the polarization rotator is rotated by 90.degree. before
reaching the birefringent lens element. The birefringent lens
element may be formed from a liquid crystal polymer or other
polymer having a liquid crystal additive to enhance birefringence
or may be formed from a polished birefringent crystal.
Tunable lenses may be formed from a stack of multiple tunable focal
length lenses. Polymer layers may be formed over lenses and may
have indices of refraction that are selected to adjust the optical
properties of the lenses. In polymer liquid crystal lenses,
alignment layers or electrodes may be used to align liquid crystal
material in desired orientations during polymer curing.
The polarization rotator may be a liquid crystal polarization
rotator such as a twisted nematic (TN) liquid crystal polarization
rotator. Control circuitry in the optical system can adjust
polarization rotators and therefore lens focal length using control
signals while creating synchronized images on a display.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of an illustrative optical system having a
tunable lens in accordance with an embodiment.
FIG. 2 is perspective view of an illustrative tunable lens having a
polarization rotator and a birefringent lens in accordance with an
embodiment.
FIG. 3 is a cross-sectional side view of an illustrative tunable
liquid crystal lens in accordance with an embodiment.
FIG. 4 is a cross-sectional side view of an illustrative lens
having a stack of two tunable lenses in accordance with an
embodiment.
FIG. 5 is a diagram showing operations and structures associated
with forming a liquid crystal lens in accordance with an
embodiment.
FIG. 6 is a cross-sectional side view of an illustrative liquid
crystal lens with ring-shaped concentric electrodes for applying
electric fields to liquid crystal material in the lens in
accordance with an embodiment.
FIG. 7 is a top view of an illustrative liquid crystal lens in
accordance with an embodiment.
FIG. 8 is a cross-sectional side view of an illustrative tunable
birefringent lens formed from a polished birefringent material in
accordance with an embodiment.
DETAILED DESCRIPTION
An illustrative optical system of the type that may be provided
with tunable optical structures is shown in FIG. 1. As shown in
FIG. 1, optical system 10 may include a tunable lens such as
adjustable lens 14. Lens 14 may include one or more lens elements
(lenses) and may be adjusted electrically based on control signals
received from control circuitry 12. Control circuitry 12 may
include storage and processing circuitry for supporting the
operation of system 10. The storage and processing circuitry may
include storage such as hard disk drive storage, nonvolatile memory
(e.g., flash memory or other electrically-programmable-read-only
memory configured to form a solid state drive), volatile memory
(e.g., static or dynamic random-access-memory), etc. Processing
circuitry in control circuitry 12 may be used to control the
operation of system 10. The processing circuitry may be based on
one or more microprocessors, microcontrollers, digital signal
processors, baseband processors, power management units, audio
chips, application specific integrated circuits, etc. System 10 may
form all or part of an electronic device such as a camera, a
projector, a display (e.g., a head mounted display), an embedded
system such as a system in an automobile, airplane, or other
vehicle, a cellular telephone, a computer, or other electronic
equipment. For example, system 10 may be a system that displays
images to a user such as user 20.
To control the operation of system 10, system 10 may be provided
with input-output devices 28. Input-output devices 28 be used to
allow data to be supplied to system 10 and to allow data to be
provided from system 10 to external devices. Input-output devices
28 may include buttons, joysticks, scrolling wheels, touch pads,
key pads, keyboards, microphones, speakers, tone generators,
vibrators, cameras, sensors, light-emitting diodes and other status
indicators, data ports, etc. A user can control the operation of
system 10 by supplying commands through input-output devices 28 and
may receive status information and other output from system 10
using the output resources of input-output devices 28.
System 10 may include one or more displays such as display 16.
Display 16 may be a liquid crystal display, an organic
light-emitting diode display, a display formed from discrete
light-emitting diode dies, or a display formed using other types of
display technology. Display 16 may include an array of pixels for
displaying images for user 20 such as image 18. User 22 may view
image 18 in direction 22 through lens 14. Due to the presence of
lens 14, a virtual image such as virtual image 24 that corresponds
to image 18 on display 16 may be viewed by user 22. In the
illustrative arrangement of FIG. 1, lens 14 is located at a
distance D from user 20 that is larger than focal length f of lens
14 and is located at a distance d from display 16 that is less than
focal length f, so virtual image 24 is magnified, but other
configurations may be used, if desired. Display 16 may be opaque or
may be transparent (e.g., display pixels may be formed on
transparent substrates) so that real-life objects such as
illustrative object 26 (e.g., a building, road, household object,
or other object) may be viewed by user 20 through display 16 in
addition to the images produced by display 16.
The properties of lens 14 may be adjusted to adjust the appearance
of virtual image 24. For example, the focal length of lens 14 may
be adjusted. In systems such as head-up displays (e.g., augmented
reality or virtual reality displays), the focal length of lens 14
may be adjusted to reduce or eliminate vergence-accommodation
mismatch. Other types of systems may also use lens focal length
adjustments. In general, an adjustable-focal-length lens such as
lens 14 of FIG. 1 may be used in any suitable optical system in
which it is desired to change the focal length properties of a
lens. The use of lens 14 in a system of the type shown in FIG. 1 in
which lens 14 is interposed between a display such as illustrative
transparent display 16 and user 20 is merely illustrative.
Lens 14 may have optical components of the type shown in FIG. 2. In
particular, lens 14 may have a polarization rotator such as
polarization rotator 14A and a birefringent lens element such as
birefringent lens 14B. Optical system 10 may have a linear
polarizer such as polarizer 30. Polarizer 30 may polarize light
from display 16 and/or light from objects in the user's environment
such as object 26. With one illustrative configuration, linear
polarizer 30 is formed as the uppermost layer in display 16. In
general, linear polarizer 30 may be associated with any suitable
structure in optical system 10 and need not be incorporated into a
display.
Control circuitry 12 may adjust the polarization rotation
properties of polarization rotator 14A so that lens 14 exhibits
either a first focal length fo or a second focal length fe<fo.
This adjusts the position at which light 32 is focused in the
example of FIG. 2. In the FIG. 2 example, birefringent lens 14B has
an ordinary index of refraction no that is aligned with dimension Y
and an extraordinary index of refraction ne that is aligned with
dimension X. Linearly polarized light 32 that is being received by
rotator 14A has an electric field that is aligned with dimension X.
After passing through rotator 14A, light 32 passes through
adjustable lens 14 and is focused at point Pe or Po.
Polarization rotator 14A has two different states. When control
circuitry 12 places polarization rotator 14A in its first state,
polarization rotator 14A will not rotate the polarization of light
32 (i.e., electric field E of light 32 will remain aligned with
dimension X). In this situation, light 32 will experience an index
of refraction of ne when passing through lens 14B and the focal
length of lens 14B will be fe. Light 32 will therefore focus at
point Pe. When control circuitry 12 places polarization rotator 14A
in its second state, polarization rotator 14A will rotate the
polarization of light 32 by 90.degree. about axis Z (i.e., electric
field E of light 32 will rotate out of alignment with dimension X
and into alignment with dimension Y). In this situation, light 32
will experience an index of refraction of no when passing through
lens 14B and the focal length of lens 14B will be fo. Light 32 will
therefore focus at point Po.
Lens structures such as polarization rotator 14A and birefringent
lens element 14B may be stacked on top of each other and may, if
desired, be stacked in groups (i.e., lens 14 may be formed from
multiple pairs of polarization rotators and birefringent lenses).
In this way, the overall properties of lens 14 may be altered for
different applications (e.g., the focal length of lens 14 may be
shortened by stacking additional lenses). Stacked lens systems may
also exhibit additional tuning states. For example, in a stacked
lens system having a first tunable lens with two focal lengths and
a second tunable lens with two focal lengths, the stacked lens
system may exhibit four selectable focal lengths.
Polarization rotator 14A may be formed from a liquid crystal
polarization rotator structure or other suitable polarization
rotator device. Birefringent lens 14B may be formed from a
birefringent crystal (e.g., calcite), may be formed from a
birefringent liquid crystal lens, or may be formed from any other
suitable birefringent lens structure.
As shown in the illustrative configuration of FIG. 3, polarization
rotator 14A may be formed from a liquid crystal polarization
rotator such as a twisted nematic liquid crystal polarization
rotator and birefringent lens 14B may be formed from a liquid
crystal lens structure.
In the example of FIG. 3, lens 14 has clear substrates such as
substrates 34 and 46. Substrates 34 and 36 may be formed from
transparent materials such as clear glass or plastic. Transparent
electrodes such as electrodes 36 and 44 may be formed from a
transparent conductive material such as indium tin oxide and may
receive electrical signals from control circuitry 12 to control the
electric field across liquid crystal layer 40. Electrode 36 may be
formed on the surface of substrate 34 that faces liquid crystal
layer 40. Electrode 44 may be formed on the surface of substrate 46
that faces liquid crystal layer 40. Liquid crystal alignment layers
such as layers 38 and 42 may be formed on electrodes 36 and 44.
Layer 38 may be interposed between electrode 36 and layer 40. Layer
42 may be interposed between electrode 44 and layer 40.
Alignment layers 38 and 42 may be formed from polyimide or other
suitable material that has been processed to form surfaces that
help align the liquid crystals of layer 40 in a desired direction.
With one suitable arrangement, layers 38 and 42 may be formed from
photosensitive polymer (e.g., polyimide) that is exposed to
linearly polarized ultraviolet light during curing. Other processes
may be used for forming liquid crystal alignment layers for
polarization rotator 14A, if desired.
When liquid crystal layer 40 is placed between alignment layers 38
and 42, the liquid crystals of layer 40 will be aligned in an
orientation determined by the properties of alignment layers 38 and
42. In the absence of an applied electric field across electrodes
36 and 44, the liquid crystals of layer 40 will not be rotated away
from their default alignment and light 32 that passes through
polarization rotator 14A will be emitted as light 32-2 having a
polarization direction (electric field orientation) aligned with
axis X (as an example). Light 32-2 will experience index of
refraction ne when passing through birefringent lens 14B. When an
electric field is applied across electrodes 36 and 44 by control
circuitry 12, polarization rotator 14A will rotate the polarization
of light 32. In particular, the liquid crystals of layer 40 will be
rotated in response to the electric field so that layer 40 will, in
turn, rotate the polarization of light 32 by 90.degree. into
alignment with axis Y (i.e., light 32 will be emitted as light 32-1
having a polarization aligned with axis Y). Light 32-1 will
experience index of refraction no when passing through birefringent
lens 14B. Accordingly, lens 14B and therefore lens 14 will exhibit
different focal lengths depending on the setting of polarization
rotator 14B.
Lens 14B of FIG. 3 may be formed from a birefringent material such
as an ultraviolet-light-curable liquid crystal polymer with an
optional liquid crystal additive to enhance birefringence. The
liquid crystal polymer may initially be dispensed in an uncured
liquid monomer state and may fill a lens-shaped cavity between
layer 54 and substrate layer 48. Layers 48 and 54 may be clear
layers formed from glass, polymer, or other clear material. For
example, layer 54 may be formed from polymer. Alignment layers may
be formed on the inner surfaces of the lens cavity. For example,
alignment layer 52 may be formed on the lower surface of layer 54
and alignment layer 48 may be formed on the upper layer of
substrate 46. Alignment layers 52 may be formed by exposing
photosensitive polymer such as a photosensitive polyimide to
linearly polarized ultraviolet light during curing of the polyimide
from a liquid polymer precursor or may be formed using other
suitable alignment layer formation techniques. The presence of
alignment layers 52 and 48 aligns the liquid crystal material of
lens layer 50 in a desired direction and thereby gives rise to a
desired birefringence (differing indices no and ne) in layer 50.
Ultraviolet light may be applied to layer 50 to cure and thereby
solidify layer 50 (i.e., to convert layer 50 from its liquid
monomer form into a solid polymer birefringent material).
The index of layer 54 and the birefringent properties of layer 50
may be selected to provide lens 14B with desired optical
characteristics. With one suitable arrangement, layer 50 may be
formed from an ultraviolet-light-cured polymer such as RM257 (e.g.,
a liquid crystal polymer) and layer 54 may be formed from a polymer
(e.g., an ultraviolet-light-cured polymer) such as
polymethylmethacrylate (PMMA). In a configuration in which the
index of refraction of layer 54 is equal to ordinary index no of
layer 50, lens 14B will exhibit a focal length of infinity (when
the polarization of light 32 is aligned with axis Y) and a finite
focal length when the polarization of light 32 is aligned with axis
X). If the index of refraction of layer 54 is greater than ordinary
index no of layer 50, lens 14 will, depending on the polarization
of light exiting rotator 14A, have a first focal length that is
negative (lens 14B will act as a concave lens) or will have a
second focal length that is either positive or negative. If the
index of refraction of layer 54 is less than no, lens 14B will act
as a convex lens with two focal lengths (depending on the
polarization of light from rotator 14A).
In the example of FIG. 3, substrate 46 serves both as a substrate
for alignment layer 44 (and electrode 44) and as a substrate for
alignment layer 48. If desired, multiple substrate layers may be
used to form layer 46 (e.g., multiple layers of glass and/or
plastic).
The thickness of liquid crystal layer 40 in polarization rotator
14A may be 1-10 microns, less than 50 microns, less than 20
microns, less than 5 microns, more than 1 micron, or other suitable
thickness. When the thickness of liquid crystal layer is
sufficiently thin, the tuning speed of rotator 14B may be high
(e.g., 5 ms, less than 10 ms, more than 1 ms, or other suitable
amount).
As shown in FIG. 4, lens 14 may include multiple stacked tunable
lenses. In the FIG. 4 example, lens 14 includes first tunable lens
14-1 with polarization rotator 14A-1 and birefringent lens 14B-1
and second tunable lens 14-2 with polarization rotator 14A-2 and
birefringent lens 14B-2. In general, adjustable focal length lens
14 may include any suitable number of stacked adjustable lenses
(one or more, two or more, three or more, etc.). In configurations
with more stacked lenses, lens 14 can be adjusted to produce
correspondingly larger numbers of focal lengths. For example in a
two-lens stacked lens arrangement of the type shown in FIG. 4, lens
14-1 may be adjusted to produce focal length fa or focal length fb
and lens 14-2 may be adjusted to produce focal length fc or fd. By
cycling through different combinations of focal length (e.g.,
fa/fc, fa/fd, fb/fc, and fb/fd), lens 14 may exhibit four different
focal lengths.
The ability to switch the polarization rotators of lens 14 at
relatively high speeds (e.g., on the order of kHz) may allow lenses
such as stacked lens 14 of FIG. 4 to exhibit each of its different
focal lengths in rapid succession. The images produced by display
16 (e.g., image frames) may be synchronized with these focal length
changes, so that different images may be rendered by system 10 at
different apparent distances from user 20 while minimizing or
eliminating vergence accommodation mismatch.
Illustrative operations associated with forming birefringent liquid
crystal lenses are shown in FIG. 5. Initially, a liquid
ultraviolet-light-curable polymer for forming layer 54 may be
deposited over mold 56. Mold 56 may have lens-shaped protrusions.
The liquid polymer of layer 54 may be cured by application of
ultraviolet light 58 or may be cured using other curing techniques
(catalyst, elevated temperature, room temperature curing,
etc.).
After curing the polymer of layer 54 to solidify layer 54, layer 54
may be removed from mold 56.
Layer 54 and associated substrate layer 46 may then be coated with
alignment layers 52 and 48, respectively and may be sandwiched
together to form a lens cavity that receives layer 50 (e.g., an
ultraviolet-light-curable liquid polymer such as a liquid crystal
polymer with an optional liquid crystal additive for enhancing
birefringence). While the liquid crystals of layer 50 are being
aligned by alignment layers 48 and 52, the polymer material of
layer 50 may be cured. For example, ultraviolet light 58 may be
applied to layer 50 to cure layer 50 and thereby lock the
birefringence of layer 50 in place. Lens 14B may then be peeled
away from substrate 46 (or may be left in place on substrate 46)
and may be assembled with rotator 14A to form a tunable lens.
FIG. 6 shows how lens 14B may be formed by using patterned
electrodes to rotate the liquid crystals of layer 50 during polymer
curing. As shown in FIG. 6, lens 14B may have a curable
birefringent layer such as layer 50 that is formed between
transparent substrates 62 and 66 (e.g., glass or plastic layers).
Transparent electrode 64 (e.g., an indium tin oxide layer) may be
formed on the surface of substrate 66 that faces layer 50. A set of
patterned electrodes 60 may be formed on the surface of substrate
62 that faces layer 50. Layer 64 may be a blanket film that covers
the surface of substrate 66. Electrodes 60 may form a series of
concentric rings such as illustrative rings 60-1, 60-2, and 60-3.
There may be any suitable number of rings in electrodes 60 (e.g.,
five or more, ten or more, twenty or more, etc.). Each ring-shaped
electrode may receive a different respective voltage (see, e.g.,
voltages V0, V1, and V2 in the example of FIG. 6) and may therefore
rotate the liquid crystals in a respective underlying portion of
layer 50 by a correspondingly different amount. By appropriate
selection of the voltages of the ring-shape electrodes, the index
of refraction of layer 50 may be progressively varied as a function
of radial distance R from center CNT of lens 14B, thereby providing
lens 14B with a desired index of refraction profile and focal
length. Birefringence may be imparted to lens 14B using an
asymmetric configuration for electrodes 60, using alignment layers,
etc. The polymer material of layer 50 may be cured by application
of ultraviolet light to layer 50 while the voltages are applied to
electrodes 60. After layer 50 has been cured in this way, the
voltages on electrodes 60 may be removed. A top view of
illustrative electrodes 60-1, 60-2, and 60-3 of FIG. 6 is shown in
FIG. 7.
If desired, lens 14B may be formed from a polished solid
birefringent material such as calcite or other birefringent
crystal. This type of arrangement is shown in FIG. 8. As shown in
FIG. 8, lens 14 may include polished birefringent crystal 68 having
a desired shape for forming lens 14B and may include polarization
rotator 14A. Polarization rotator 14A may be, for example, a
twisted nematic liquid crystal polarization rotator of the type
described in connection with FIG. 3 or may be any other type of
polarization rotator. If desired, an optional layer of material
such as layer 70 may be applied to the upper surface of lens
element 68. As described in connection with layer 54 of FIG. 3, the
index of refraction of layer 70 may be the same as the ordinary
index of refraction no of lens element 68 or may be greater or less
than index no. Lenses of the type shown in FIG. 8 may be stacked
with other adjustable lenses and may be incorporated into an
optical system such as optical system 10 of FIG. 1 or other
suitable optical system, as described in connection with FIG.
4.
The foregoing is merely illustrative and various modifications can
be made by those skilled in the art without departing from the
scope and spirit of the described embodiments. The foregoing
embodiments may be implemented individually or in any
combination.
* * * * *
References